A semiconductor device is fabricated by placing it in a processing chamber in which device layers are formed, processing residue is removed, and other processing steps are performed on it. In addition, certain processing chambers are used for cleaning semiconductor wafers at supercritical temperatures and pressures.
Generally, processing chambers contain an upper element and a lower element. When the two elements are brought together, they form a processing volume in which a wafer is contained during processing. During processing, it is critical that the processing volume remain sealed so that it can be maintained at correct operating conditions, such as high-pressure, atmospheric, or supercritical conditions. Sealing the processing volume from the outside environment also ensures that (a) the processed wafer is not exposed to contaminants, making it unusable, and (b) processing materials, such as harmful chemicals, introduced into the processing volume are not released to the surroundings.
A processing volume is maintained by applying a sealing force to counteract a processing force generated within the processing volume while the wafer is being processed. The processing force acts to force the upper element and the lower element apart, opening the processing volume seal and breaking the processing volume. The sealing force may be produced by a hydraulic piston. To ensure that the processing volume is maintained regardless of the processing force, before the workpiece is processed the sealing force is set to the largest attainable processing force. The sealing force remains at this level even if the largest attainable processing force is never reached or is reached for only a small portion of the entire processing cycle.
Such processing chambers have several disadvantages. First, sealing components that bear the highest attainable sealing force for an unnecessary length of time are prone to failure after repeated applications of the sealing force. Second, the large contact forces on the sealing face produce particulates that are introduced into the processing volume and contaminate the wafer. Third, the equipment used to pressurize the hydraulic fluids adds costs to the processing system, since the equipment is used to seal the processing chamber and not to process a wafer. Fourth, those systems that could be designed to replace hydraulic components with supercritical components using supercritical processing materials are expensive. These systems require complicated recycling techniques because the supercritical processing materials must be expanded and pressurized before they can be reused.
Accordingly, what is needed is a processing system that (1) does not require a continuous excessive sealing force to maintain a processing volume, (2) reduces the number of contaminants that may be introduced into the processing volume, (3) uses elements already used in processing for maintaining the processing volume seal, and (4) uses a small energizing volume so that the processing system is compact and operates more efficiently.